Neuronal connectome of a sensory-motor circuit for visual navigation

Animals use spatial differences in environmental light levels for visual navigation; however, how light inputs are translated into coordinated motor outputs remains poorly understood. Here we reconstruct the neuronal connectome of a four-eye visual circuit in the larva of the annelid Platynereis using serial-section transmission electron microscopy. In this 71-neuron circuit, photoreceptors connect via three layers of interneurons to motorneurons, which innervate trunk muscles. By combining eye ablations with behavioral experiments, we show that the circuit compares light on either side of the body and stimulates body bending upon left-right light imbalance during visual phototaxis. We also identified an interneuron motif that enhances sensitivity to different light intensity contrasts. The Platynereis eye circuit has the hallmarks of a visual system, including spatial light detection and contrast modulation, illustrating how image-forming eyes may have evolved via intermediate stages ...

动物可借助环境光照水平的空间差异完成视觉导航，但目前学界对光照信号如何转化为协调的运动输出仍缺乏深入认知。本研究通过连续切片透射电子显微镜（serial-section transmission electron microscopy），重构了环节动物多鳞沙蚕（Platynereis）幼虫体内四眼视觉环路的神经元连接组（neuronal connectome）。该环路共包含71个神经元，光感受器通过三层中间神经元与支配躯干肌肉的运动神经元相连。研究人员结合眼球摘除术与行为学实验证实，该环路可比对躯体两侧的光照水平，并在视觉趋光性（visual phototaxis）过程中，当双侧光照失衡时触发躯体弯曲动作。本研究还鉴定出一类中间神经元基序，可提升对不同光照强度对比度的敏感度。多鳞沙蚕的视觉环路具备视觉系统的典型特征，包括空间光检测与对比度调制功能，这为解析成像眼如何通过中间演化阶段逐步起源提供了重要启示……